1. Field of the Invention
The present invention relates to a tissue paper used for heat-sensitive stencil sheet, a heat-sensitive stencil sheet, and a method of fabricating the same. More specifically, the present invention relates to a high quality of heat-sensitive stencil sheet to be perforated with irradiation of infrared light or flash light from a halogen lamp, a xenon lamp, or a flash bulb, pulsed irradiation of laser light, or heat irradiation from a thermal head, and a method of fabricating the same at less cost.
2. Description of the Related Art
There are generally known heat-sensitive stencil sheets, in which tissue papers used are (1) a paper as called Japanese paper which is milled from a natural fiber such as mulberry, mitsumata, or Manila hemp (as disclosed in Japanese Examined Patent Publication of Tokkou Shou 41-7623,(2) a paper milled from a synthetic fiber such as rayon, vinylon, polyester, or nylon, (3) a mixture milled paper of the natural fiber (1) and the synthetic fiber (2) (as disclosed in Japanese Examined Patent Publication of Tokkou Shou 49-18728, and (4) a tissue paper called polyester paper which is made by a polyester fiber or a mixture of it and non-oriented polyester fiber as a fibrous binder, and formed by the use of heat rolls, as disclosed in Japanese Examined Patent Publication of Tokkou Shou 49-8809.
As these tissue papers are deflected in shape or changed in dimensions by moisture or temperature thus declined in their properties, the improvements were proposed that include an effort for minimizing the dimensional change in the humid conditions, as disclosed in Japanese Unexamined Patent Publication of Tokkai Shou 61-254396 and Japanese Examined Patent Publication of Tokkou Shou 06-43151, or a use of a synthetic resin impregnated in tissue to act as an adhesive for bonding between the tissue and a film, as disclosed in Japanese Examined Patent Publication of Tokkou Shou 55-47997. Also, methods of fabricating polyester paper having an improved dimensional stability and the resistance to heat are proposed as disclosed in Japanese Unexamined Patent Publication of Tokkou Shou 58-76597 and Japanese Unexamined Patent Publication of Tokkou Shou 58-76598.
Moreover, proposed are a method of fabricating a heat-sensitive stencil sheet impregnated with a radiation-curable of ionizing radiation-curable type, in which a thermoplastic resin film and a tissue paper used for heat-sensitive stencil sheet are bonded each other by an resin of the ionizing radiation-curable resin, as disclosed in Re-publication by Japanese Language of PCT Application of Kokusaihyou Hei 1-801872, or a method of fabricating a heat-sensitive stencil sheet which comprises steps of bonding and laminating a thermoplastic resin film and a tissue paper together with an alcohol solution of an ionizing radiation-curable type of polymer or oligomer and, after drying, exposing a resultant combined web to ultraviolet ray or electron beam for reinforcement, as disclosed in Japanese Unexamined Patent Publication of Tokkai Hei 01-154796.
However, the foregoing conventional methods do not yet satisfy the primary requirements for any heat-sensitive stencil sheet such as; (1) an excellent passing-through of printing ink, (2) the ease of perforation, (3) no releasing of the fibers, (4) the resistance to printing action, and (5) the high productivity.
The conventional tissue papers for heat-sensitive stencil sheet, the heat-sensitive stencil sheets, and their fabricating methods have the following drawbacks.
As common, the conventional tissue papers for heat-sensitive stencil sheet including natural fibers are impregnated with a resin material by a known manner for preventing a change in dimensions thereof, which is caused by absorbing to and removing from of the moisture the natural fibers, and liberating of the fibers from tissue papers. Accordingly, the tissue paper may easily be deformed by a stress applied during bonding of it with the thermoplastic resin film, and after that, if it is released from its stressed state, it springs back to its original dimensions, in spate of having been bonded with the thermoplastic resin film, thereby it will cause a degrading in the surface smoothness of the thermoplastic resin film, and it will hence be found difficult to control the laminating action.
Although conventional tissue paper used for heat-sensitive stencil sheet made of a synthetic fiber material is subjected to heat-pressing process for increasing the bonding strength between the fibers, it may be increased in the density while having no removal of the fibers, hence declining the passing-through of printing ink. On the contrary, if the tissue paper is pressed down at a lower temperature, though it is improved in passing-through of ink, it may have the fibers removal. For compensating these problems, the conventional tissue paper used for heat-sensitive stencil sheet can favorably be reinforced with a resin material, however, as the synthetic fibers are lower than the natural fibers in the physical strength, the above described disadvantage will more be emphasized with the synthetic fiber contained in tissue paper.
There is known method for producing a heat-sensitive stencil sheet supported by a tissue paper as a supporting substrate, which comprises steps of placing the two kinds of material layers in integrated form of plastic resin and tissue paper, then impregnating them at once with resinous solution to make impregnated them with resin, drying and exposing to ionizing radiation ray or electron beam for bonding with each other allows the combined web being favorably controlled. By this method, the controlling of the laminating is case, however, as the resin is diluted in a solution for easy application thereof, there is found difficult problem of the tendency that the resin solution is concentrated at the interface between the thermoplastic resin film and the contact end of the tissue paper as shown in FIG. 1. This interrupts the perforation of the thermoplastic resin film, and causes no sharp print images.
For implementing high quality prints, there is provided method of fabricating a heat-sensitive stencil sheet, in which a porous resin layer is provided between the thermoplastic resin film and the tissue paper. However, the use of a solution diluted with solvent is also questioned because it enters in and plugs up the pores in the porous resin layer. Also, if the solvent is an organic material, it may dissolve the porous resin layer itself.
In case that the thermoplastic resin film and the tissue paper used for heat-sensitive stencil sheet are bonded each other by an ionizing radiation-curable resin, the tissue paper used for heat-sensitive stencil sheet has to be impregnated with the ionizing radiation-curable resin for controlling laminating action, otherwise results the difficulty in controlling of above mentioned laminating.